A throttle valve is disposed in an air-intake passage coupled to an engine mounted in a two-wheeled motor vehicle, etc., and is configured to control the amount of air supplied to the engine. A rider manually operates a throttle operation device such as an accelerator pedal, an accelerator grip (throttle grip), or a throttle lever to move the throttle valve.
An electronic control throttle system is typically configured in such a manner that the throttle valve is controlled by a so-called drive-by-wire system. To be specific, upon the rider operating the throttle operation device, a position sensor attached to the throttle operation device detects the operation amount of the throttle operation device, and sends a detection signal to a controller, for example, an electronic control unit (ECU). Receiving the detection signal, the ECU determines a target opening degree of the throttle valve, and sends a signal indicating the target opening degree to a throttle valve computer (TVC). Based on the target opening degree signal, the TVC causes a drive unit, for example, an actuator such as a DC motor, to actuate the throttle valve.
A throttle position sensor attached to the throttle valve detects an actual opening degree of the throttle valve, and sends a detection signal to the TVC. The TVC sends a control signal to the actuator in order to compensate for a deviation between the target opening degree and the actual opening degree. In this manner, the throttle valve is moved to the opening degree so as to precisely respond to the operation of the throttle operation device, thus controlling the amount of air to be supplied to the engine.
Typically, in such throttle valve control, occurrence of overshooting in which the throttle valve is moved to an opening degree that is beyond its target opening degree (e.g., fully open position) is inhibited. If the overshooting occurs, the actual throttle opening degree undesirably fluctuates, so that an engine speed fluctuates according to the fluctuation of the amount of air. To inhibit this, control is executed to inhibit the occurrence of the overshooting. Such a technique is disclosed in, for example, Japanese Laid-Open Patent Application Publication No. Hei. 4-183644.
In order to inhibit the occurrence of the overshooting in PID control, PD control, etc., a proportional gain is typically set smaller. By setting a derivative gain larger, a convergence property of the throttle valve in a fully open position is improved. Concurrently with or in addition to this, a mechanical stopper may be mounted at the fully open position of the throttle valve to set a mechanical fully open position.
However, in the throttle valve control that is directed to improving the convergence property in the fully open position, responsiveness of the throttle valve opening degree to quick operation of the throttle operation device is low. Even if the throttle operation device is quickly operated to quickly move the throttle valve to the fully open position to thereby rapidly increase an engine speed, the throttle valve is actually not moved at a desired speed. In the case where the mechanical stopper defines the fully open position of the throttle valve, a problem that an impact is applied to a motor of the actuator, a gear system, the mechanical stopper, and so on, may arise. In a substantially fully open position of the throttle valve, the amount of air does not substantially fluctuate regardless of the fluctuation in the opening degree of the throttle valve.